Hi J.,
We also did this test with our now 2 year old daughter. It was fine, no problems and it's really not a difficult test, other than keeping your child as still as possible for a few minutes. (I know, easier said than done!) I wouldn't stress it though, it's not a big deal.
I really don't have alot of answers for you as we are stuggling with the very same thing as you. I will say, you might look into seeing someone who specializes in "sensory disorders." Or at least google "SPD" online and see if your child fits any oth the descriptions at all. Our docs and specialists are thinking that our daughter has this and all it is, is basically the way a child takes in information through the 5 senses. There is sometimes a brain disconnect between the outside info they receive and then how they respond to that. If your child is over-sensitive for example, and there is a more technical term for it that I can't remember, eating will be an issue for him. Our daughter still can't eat meat without gagging and will only eat soft or pureed foods. She has a specialist that comes every week to help her learn how to talk and eat etc.
With help from a specialist, they tell me that they can grow out of these issues. Take heart, if that's what you have to do it's really not the end of the world. We've received alot of help from our guy. Some kids just need some extra help and if there isn't anything physically wrong with his eating organs, places like "SoonerStart" will help your family for free.